Cancer is a worldwide problem that afflicts millions of people each year. As such, finding methods for its treatment is of vital interest. Both chemotherapy and radiation are used in the treatment of cancer. Chemotherapy refers to the use of chemical compounds or drugs in the treatment of disease, though the term chemotherapy is most often associated with the treatment of cancer. Cancer chemotherapeutic agents are also commonly referred to as antineoplastic agents. The severe side effects experienced with the majority of cancer chemotherapeutics are a result of the non-specific nature of these drugs, which do not distinguish between healthy and cancerous cells, and instead destroy both. The cell cycle specific drugs attempt to lessen these effects, targeting phases of the cell cycle involved in cell replication and division. These drugs do not, however, distinguish between cancerous cells and healthy cells which are undergoing normal cell division. The cells most at risk from these types of chemotherapy are those which undergo cell division often, including blood cells, hair follicle cells, and cells of the reproductive and digestive tracts.
The most common side effects of chemotherapeutic agents are nausea and vomiting. A large proportion of individuals also suffer from myelosuppression, or suppression of the bone marrow, which produces red blood cells, white blood cells and platelets. These and other side effects are also exacerbated by the suppression of the immune system concomitant with the destruction and lack of production of white blood cells, and associated risk of opportunistic infection. Other side effects common to a wide range of chemotherapeutic agents include hair loss (alopecia), appetite loss, weight loss, taste changes, stomatitis and esophagitis (inflammation and sores), constipation, diarrhea, fatigue, heart damage, nervous system changes, lung damage, reproductive tissue damage, liver damage, kidney and urinary system damage.
Radiation is another commonly used treatment for cancer, used in approximately 60% of treatment regimens. Often combined with chemotherapy and/or surgery, radiation therapy encompasses both local and total body administration as well as a number of new advances, including radioimmunotherapy. The cytotoxic effect of radiation on neoplastic cells arises from the ability of radiation to cause a break in one or both strands of the DNA molecule inside the cells. Cells in all phases of the cell cycle are susceptible to this effect. However, the DNA damage is more likely to be lethal in cancerous cells because they are less capable of repairing DNA damage. Healthy cells, with functioning cell cycle checkpoint proteins and repair enzymes are far more likely to be able to repair the radiation damage and function normally after treatment.
The side effects of radiation are similar to those of chemotherapy and arise for the same reason, the damage of healthy tissue. Radiation is usually more localized than chemotherapy, but treatment is still accompanied by damage to previously healthy tissue. Many of the side effects are unpleasant, and radiation also shares with chemotherapy the disadvantage of being mutagenic, carcinogenic and teratogenic in its own right. While normal cells usually begin to recover from treatment within two hours of treatment, mutations may be induced in the genes of the healthy cells. These risks are elevated in certain tissues, such as those in the reproductive system. Also, it has been found that different people tolerate radiation differently. Doses that may not lead to new cancers in one individual may in fact spawn additional cancers in another individual. This could be due to pre-existing mutations in cell cycle checkpoint proteins or repair enzymes, but current practice would not be able to predict at what dose a particular individual is at risk. Common side effects of radiation include bladder irritation, fatigue, diarrhea, low blood counts, mouth irritation, taste alteration, loss of appetite, alopecia, skin irritation, change in pulmonary function, enteritis, sleep disorders, and others.
Chemotherapy treatment and a radiation therapy may be combined in the treatment of cancers but often the patient suffers increased risk due to the cumulative side-effects and toxicity of each treatment. A synergistic effect allows for less exposure to toxic chemotherapeutic agents and radiation therapy, thereby reducing side-effects, while achieving an improved beneficial result.